The invention relates to a pulse radar apparatus for target tracking, which radar apparatus is designed to provide angular error data representing the deviations of projectiles, fired from a gun at the target with respect to the target position line. By "targets" are meant in particular self-propelled missiles, whereas the gun-fired projectiles are preferred to follow a ballistic trajectory.
Such a pulse radar apparatus is known from the U.S. Pat. No. 3,201,788. In the radar apparatus described in this specification, two auxiliary range gates placed at both sides of the target range gate are positionable in accordance with the displacement of the target range gate, so that each of them passes exclusively echo signals, in particular from the gun-fired projectiles, in the range intervals corresponding with the two auxiliary range gates. These echo signals are used to measure the deviations of the projectiles with respect to the antenna line of sight in passing through the range intervals; subsequently, the deviations of the projectile prevailing at the target position are determined by interpolation. The above patent specification emphasises that, to obtain accurate angular error data about the deviations of the gun-fired projectiles prevailing at the target with respect to the target position line, it is not very well possible to use the projectile echo signals passed through the target range gate, as these signals cannot be distinguished from the target echo signals. The indicated determination of the desired angular error data has the disadvantage that the curved path described by the projectiles between the two auxiliary range gates is approximated by a straight line, resulting in incorrect values of the angular errors. Besides, there is a cumulation of errors due to the parallax between the pulse radar apparatus and the gun, making accurate computation of the angular errors by the method of interpolation very complicated. The present invention has for its object to provide a solution to these problems, which solution is based on the measurement of echo signals received from both the target being tracked and the gun-fired projectiles in the same range gate, i.e. the target range gate.